First report of Alternaria tenuissima causing leaf spot and fruit rot on eggplant (Solanum melongena) in India

A leaf spot disease of eggplant (Solanum melongena) was observed during 1997-2000 in Guntur district Andhra Pradesh, India. The symptoms recorded were small, circular, brown necrotic spots all over the foliage. The spots gradually enlarged in size and later became irregular in shape or remained circular with concentric rings or zones (Fig. 1). In the later stage of infection, these spots coalesced resulting in withering, extensive drying and shedding of leaves. On fruit, the symptoms started as small concentric dark brown sunken spots, which coalesced and covered the entire surface of the fruit (Figs 2 & 3). Affected fruit rotted completely, causing severe yield losses.

The causal agent of this disease was successfully isolated on potato dextrose agar (PDA) from the diseased leaves and fruits. After 4 to 5 days of incubation at 26°C with a 12 h photoperiod, the fungus produced colonies which were regular and flat, with a rough upper surface. The periphery of the colony was olive-green, with a black centre and dull white spots. The growth of the fungus was smooth. The conidiophores were short, arising singly measuring 81.6 to 163.2 mm in length and were 4.08 to 8.16 mm thick. The size of the conidia varied from 26 to 48.75 mm in length and 9.75 to 16.27 mm in width, with an average beak length of 9.58 mm. Horizontal and vertical septations of conidia varied from 1 to 6 and 0 to 2 respectively. On the basis of the morphological characteristics of the conidiophores and conidia, the pathogen was identified as Alternaria tenuissima (Fig. 4). The culture was sent to the Indian type culture collection, located at Indian Agricultural Research Institute in New Delhi, who confirmed the identity of the isolate as Alternaria tenuissima.

Pathogenicity tests were conducted on 60-day-old egg plants (cv. Bapatla Local) by spraying with a spore suspension (5x10⁵ spores per ml) using an atomizer in the late evening. Inoculated plants were covered with a polythene bag and incubated at 26°C with a 14 h photoperiod. Thirty days after inoculation, the symptoms were similar to those previously observed. A. tenuissima was consistently re-isolated from the inoculated plants. At the same time control leaves, sprayed with distilled water, did not develop any symptoms. A. tenuissima is a cosmopolitan fungus already identified in India on several hosts e.g. taro (Colocasia esculenta; Solankure & Rao, 1972, pigeon pea (Cajanus cajan; Kannaiyan & Nene, 1977) and Ipomoea carnea (Reddy & Rao, 1975). It is a first record on eggplant in India.